Followup: Rename `type` column to `categroy` for audit destinations

We have two tables, audit_events_group_external_streaming_destinations and audit_events_instance_external_streaming_destinations, which have an enum field type which is being used for storing the type of external audit event destination. After creating these tables, I found out that there is restriction on using a field named type and it can also be used for inheritance. So, we need to rename the field to category.